This invention relates to ceramic matrix composite components in general, and specifically, to a high temperature ceramic matrix composite component that incorporates a monolithic attachment bushing.
Ceramic matrix composites (CMC""s) offer high material temperature capability. In the gas turbine field, however, CMC components often require attachment to, or engagement with, lower temperature metallic gas turbine components. Problems associated with the attachment of known silicon carbide ceramic matrix composites (CMC""s) to metallic components include wear, oxidation (due to ionic transfer with metal), stress concentration (from clamping loads), transition to thick section fabrication, and fiber damage in creating holes in the CMC""s.
In an exemplary embodiment of the invention, advantage is taken of the very high strength of monolithic ceramics to absorb the clamping loads of bolt and pin-type attachment means. The component in one embodiment thus includes, for example, an inner core formed as an attachment bushing or a wear pad made of either silicon carbide or silicon nitride monolithic ceramic that is embedded within the body of a CMC shell. It is understood that material selection for the inner core or attachment bushing (or wear pad) depends on specific attachment requirements, and the shape of the bushing or wear pad could be any number of shapes, several of which are disclosed herein. Preferably, the shape of the bushing or wear pad would thus be optimized to insure that it is well encased within the surrounding CMC shell fabric layers, and that the load is optimally distributed into the CMC component structure. In one exemplary embodiment, the required size of a through hole in the bushing will contribute to set the overall size of the bushing in order to preserve an appropriate surface area of monolithic ceramic within the surrounding CMC shell.
In other embodiments, the through hole may be eliminated in favor of a blind hole, or even a solid center with oppositely facing wear surfaces.
The CMC shell that incorporates the bushing or wear pad may be any gas turbine or other component, and is not limited to the shape or configuration described and/or illustrated herein.
Accordingly, in its broader aspects, the present invention relates to a component for use in a gas turbine comprising an inner attachment bushing comprised of a monolithic ceramic material having front and back faces and a through-hole formed therein of predetermined diameter and adapted to receive a bolt shank or pin, the attachment bushing substantially encased within an outer shell composed of CMC material.
In another aspect, the invention relates to a gas turbine component comprising an inner attachment bushing made of silicon nitride or silicon carbide, the attachment bushing having a first outer diameter and a through-hole formed therein having a second diameter, the first diameter being 2.5-4 times the second diameter; wherein the attachment bushing is enclosed within an outer shell of ceramic matrix composite material.
In another aspect, the invention relates to a gas turbine component including an attachment bushing of silicon nitride or silicon carbide material, the attachment bushing substantially encased within an outer shell composed of CMC material, wherein the attachment bushing is formed with a through hole, opposite ends of which are flush with respective opposite sides of the outer shell.
In still another aspect, the invention relates to a method of making a gas turbine component comprising a) forming an attachment bushing of silicon nitride or silicon carbide; and b) applying a ceramic matrix composite material over substantially all of the inner core with the exception of front and rear flat faces about a center axis of the attachment bushing.